This invention is directed to devices and equipment for collecting bulk solids, for example, process dust coming from a dust generating tool, such as a sanding machine, saw, router, planer or the like, where the dust is entrained in a flow of air from the source machine, and is separated out at the dust collection equipment, which precipitates the dust precipitates into a bag, drum, barrel, or other container. The invention is more specifically directed to a compact and efficient device to be used to separate and collect the dust from the airstream emerging from the tool, and to clean and filter the air stream which is then returned to the ambient. The invention is likewise concerned with a simple and straightforward portable dust separation assembly that can be associated with a tool that has a duct from which the air stream plus the entrained dust particles proceed.
For many types of machines for processing a workpiece, some mechanism has to be provided to dispense with the grindings, chips, and particulate matter that is generated by the machine during operation. For example, in the case of wood working machines, such as saws, planers, sanders, joiners, and the like, wood dust that is removed from a workpiece has to be collected and removed from the work area so as to avoid creating either a breathing hazard for the workman or a fire hazard. More specifically, in the case of portable equipment, sanders and buffers, it is conventional to draw off the dust that is generated by the machines and then send the air that is carrying the dust into a filter bag arrangement, or to draw off the dust through a flexible hose or conduit. In such case, the conduit or hose extends from a dust outlet duct of the machine to a collection station. In the case of smaller equipment, e.g., palm sanders or trim sanders, the stream of air is pumped through a flexible hose conduit, with the entrained process dust, to a piece of equipment that provides suction and some filtering, e.g., a shop vacuum. The same problem of environmental dust arises in metal working and ceramics also.
A number of portable dust collectors for woodshop use have been proposed, which are typically known as single-stage dust collectors because they are intended to pull the dust, shavings and chips from a woodworking machine through an impeller in a single pass. In the typical example of a portable dust collector, a hose connects the collector to a dust outlet of the machine, and an airstream travels though this, with entrained dust, chips, and other particles, to the blower or impeller. The impeller, which is typically driven by a 1.5 HP 110 volt AC induction motor, moves the airflow through a tubular conduit to a cylinder that is open on its top and bottom. A lower bag of a plastic film which may include reinforcement, is disposed below the cylinder to capture large chips and shavings. Above the cylinder is a filter bag, which is intended to catch the fine dust particles and let the air flow pass through. A cartridge filter can be substituted where it is desired to trap particles down to one micron diameter. The entire unit is typically mounted on a base, e.g., a cart or platform, with wheels, rollers or casters so that the unit can be moved around the shop from one machine to another.
Because of the design, only about half the dust that is produced is separated out and falls into the lower bag, and the rest goes up to the upper filter. The upper filter tends to blind or clog after a limited operation time, which reduces the efficiency of the unit.
Also, a typical woodworking machine, such as a planer, joiner or table saw, requires an air flow of about 400 to 800 cfm to pick up all the generated dust in the air stream, and this is also the maximum air flow that these existing portable dust collector units can produce in normal operation. Consequently, for a woodworking machine that generates more dust than these machines, the air flow would not be sufficient to capture all the dust produced. However, it is not a simple matter to produce a bigger or more powerful dust collection unit of that design.
To date, a cyclonic dust collection system, in which the air flow and entrained process dust are drawn through a cyclone separator, has not been used in a portable dust collection unit. In practice, no one has attempted to use a true cyclonic separator as a dust separation and collection device between the dust producing tool and the portion of the unit where the air is filtered and returned to the ambient.
Further, the current equipment designs do not have any means for removing or loosening the collected dust particles from the filter, except to remove the filter and blast it with compressed air.